The present invention generally relates to door constructions, and more specifically to a counterforce assembly for doors which counterbalances or compensates for high pressures on one side of a door to thereby facilitate opening of the door irrespective of the absolute pressures which act on the same.
The pressures on the two sides of a door may vary substantially in certain instances. For example, a door exposed to the exterior of a structure may be exposed to high winds and other atmospheric conditions which create a pressure acting on the exterior of the door which is substantially higher than the low pressures of the interior of the structure. In such instances, it becomes difficult, if not impossible, for one or even two or more individuals to open the door against the high resulting forces. To open a door under these conditions it is necessary for the person opening the door to apply a force which is equal to the pressure differential on the two sides of the door acting over the surface area of the door.
According to a recent development, the fire codes of some large cities require that pressurization systems be provided along the stairwells of high rise buildings with the aim of preventing the spread of smoke and fire into stairwell areas. With such a system, a large blower is provided which causes a forced air flow through the stairwells. The resultant pressure, applied over area of the door, can create a force of up to one thousand pounds which must be overcome. Clearly, such high pressure applied to a fire door will prevent the opening of the same by one, or even two or more individuals. There is not known in the prior art a practical and inexpensive means for assisting the opening of doors which are subjected to high pressure differentials of the type above suggested.
The present invention is for a counterforce assembly which cooperates with a door which may be subjected to high pressure differentials. The counterforce assembly cooperates with the door, either by means of a pressure plate, a fulcrum arm, a series of linkages, a pulley arrangement, or other coupling means to apply a counterforce to the door which tends to open the latter. The counterforce which is applied to the door may be of a magnitude which is substantially equal to the magnitude of the force exerted upon the door itself. In this manner, the counterforce assembly only compensates or negates the effect of the high forces exerted by the high pressures, and permits the door to be opened by the application of a relatively small force. The small force now required need only be large enough to overcome friction at the hinges, springs or door return mechanisms. According to the broad principle of the present invention, the counterforce assembly may be dimensioned to undercompensate, fully compensate or overcompensate the forces applied to the door. Accordingly, the counterforce assembly provides substantial flexibility in the manner in which the door can be controlled. Counterforce assemblies of the type contemplated may be utilized in conjunction with fire doors where blowers are utilized or with doors which are exposed to high atmospheric pressures, such as in cyclone regions and in many other instances where high pressure differentials acting upon a door are anticipated.